Spin current magnetization reversal-type magnetoresistive effect element and method for producing spin current magnetization reversal-type magnetoresistive effect element

ABSTRACT

This spin current magnetization rotational magnetoresistance effect element includes a substrate, a magnetoresistance effect element having a first ferromagnetic metal layer in which a direction of magnetization is fixed, a nonmagnetic layer, a second ferromagnetic metal layer configured for a direction of magnetization to be changed, and a cap layer in that order from the substrate side, and a spin-orbit torque wiring extending in a direction intersecting a lamination direction of the magnetoresistance effect element and joined to the cap layer, in which the cap layer includes one or more substances having high spin conductivity selected from the group consisting of Cu, Ag, Mg, Al, Si, Ge, and GaAs as a major component.

TECHNICAL FIELD

The present invention relates to a spin current magnetization rotationalmagnetoresistance effect element and a method of manufacturing a spincurrent magnetization rotational magnetoresistance effect element.Priority is claimed on Japanese Patent Application No. 2015-232334,filed Nov. 27, 2015, Japanese Patent Application No. 2016-053072, filedMar. 16, 2016, Japanese Patent Application No. 2016-056058, filed Mar.18, 2016, Japanese Patent Application No. 2016-210531, filed Oct. 27,2016, and Japanese Patent Application No. 2016-210533, filed Oct. 27,2016, the content of which is incorporated herein by reference.

BACKGROUND ART

A giant magnetoresistance (GMR) element formed of a multilayer filmincluding a ferromagnetic layer and a nonmagnetic layer and a tunnelmagnetoresistance (TMR) element in which an insulating layer (a tunnelbarrier layer, a barrier layer) is used for a nonmagnetic layer areknown. Generally, although a TMR element has a higher element resistanceas compared with a GMR element, a magnetoresistance (MR) ratio of TMRelement is larger than an MR ratio of a GMR element. Therefore,attention is focused on the TMR element as an element for magneticsensors, high frequency components, magnetic heads, and magnetic randomaccess memories (MRAMs).

As a writing method of MRAMs, a method of performing writing(magnetization rotation) by utilizing a magnetic field generated by acurrent, and a method of performing writing (magnetization rotation) byutilizing a spin transfer torque (STT) generated by causing a current toflow in a laminating direction of a magnetoresistance element are known.

In the system using the magnetic field, since there is a limit to anamount of current flowing through a thin wiring, there is a problem inthat writing becomes impossible when a size of an element becomes small.

In contrast, in the system using the spin transfer torque (STT), oneferromagnetic layer (fixed layer, reference layer) spin-polarizes acurrent, a spin of the current is transferred to magnetization ofanother ferromagnetic layer (free layer, recording layer), and therebywriting (magnetization rotation) is performed by the torque (STT)generated at that time. Therefore, there is an advantage in that, as asize of the element becomes smaller, a current required for writing canbe smaller.

However, in the magnetoresistance effect element using the STT, it isnecessary to cause an inversion current for causing magnetizationrotation to flow in a lamination direction of the magnetoresistanceeffect element. The current flowing in the lamination directionadversely affects a life span of the magnetoresistance effect element.

Therefore, in recent years, it has been proposed that magnetizationrotation utilizing spin-orbit interaction induced by a pure spin currentcan be used for applications (for example, Non Patent Literature 1).

The magnetoresistance effect element in which the spin-orbit interactionis performed induces a spin-orbit torque (SOT) by a pure spin currentand the SOT causes magnetization rotation to occur. The pure spincurrent is generated when the same number of upward spin electrons anddownward spin electrons flow in opposite directions to each other. Sincea flow of electric charge as a whole is canceled out, an amount ofcurrent is zero even though the pure spin current flows.

The pure spin current flows in a direction perpendicular to a directionof current flow. Therefore, in the magnetoresistance effect elementusing the SOT, an inversion current for inducing magnetization rotationflows in a direction intersecting a lamination direction of themagnetoresistance effect element.

In other words, in the magnetoresistance effect element using an SOT, itis not necessary to flow a current in a lamination direction of themagnetoresistance effect element, and a prolonged life is expected.

CITATION LIST Non Patent Literature

-   [Non Patent Literature 1]-   1. M. Miron, K. Garello, G. Gaudin, P. -J. Zermatten, M. V.    Costache, S. Auffret, S. Bandiera, B. Rodmacq, A. Schuhl, and P.    Gambardella, Nature, 476, 189 (2011).

SUMMARY OF INVENTION Technical Problem

Studies for magnetoresistance effect elements using a spin-orbit torque(SOT) have just begun. Thus, a clear configuration has not beendetermined, but a top pin structure in which a free layer is provided ona substrate side is widely used.

An SOT induced by a pure spin current is greatly affected by aninterface of laminated layers. In order to obtain a large SOT,interfaces are required to be uniform. Generally, in a laminate, as alayer is closer to a substrate, influence of each layer laminatedbecomes smaller and homogeneous. Therefore, in order to efficientlysupply a pure spin current to the free layer, a top pin structure isemployed.

On the other hand, in a magnetoresistance effect element using STT, abottom pin structure is also widely employed. This is because, since afixed layer is on a substrate side, magnetization is stabilized andgeneration of noise is inhibited.

This bottom pin structure can also be applied, in principle, to themagnetoresistance effect element using the SOT. However, when the bottompin structure is actually applied to the magnetoresistance effectelement using the SOT, there is a problem in that a laminated interfaceis disturbed and a pure spin current is not efficiently supplied to thefree layer.

The present invention has been made in view of the above-describedproblems, and it is an object of the present disclosure is to provide amagnetoresistance effect element capable of efficiently utilizing an SOTinduced by a pure spin current and a manufacturing method thereof.

Solution to Problem

(1) A spin current magnetization rotational magnetoresistance effectelement according to a first aspect includes a substrate, amagnetoresistance effect element provided on the substrate and includinga first ferromagnetic metal layer in which a direction of magnetizationis fixed, a nonmagnetic layer, a second ferromagnetic metal layerconfigured for a direction of magnetization to be changed, and a caplayer in an order from the substrate side, and a spin-orbit torquewiring extending in a direction intersecting a lamination direction ofthe magnetoresistance effect element and joined to the cap layer, inwhich the cap layer includes one or more substances having high spinconductivity selected from the group consisting of Cu, Ag, Mg, Al, Si,Ge, and GaAs as a major component.

(2) In the spin current magnetization rotational magnetoresistanceeffect element according to the above aspect, a thickness of the caplayer may be equal to or less than a spin diffusion length of asubstance constituting the major component of the cap layer.

(3) The spin current magnetization rotational magnetoresistance effectelement according to a second aspect includes a magnetoresistance effectelement including a first ferromagnetic metal layer in which a directionof magnetization is fixed, a nonmagnetic layer, a second ferromagneticmetal layer configured for a direction of magnetization to be changed,and a cap layer in an order, and a spin-orbit torque wiring extending ina direction intersecting a lamination direction of the magnetoresistanceeffect element and joined to the cap layer, in which the cap layer hasspin conductivity, and the magnetoresistance effect element furtherincludes a diffusion prevention layer between the second ferromagneticmetal layer and the cap layer.

(4) In the spin current magnetization rotational magnetoresistanceeffect element according to the above aspect, the diffusion preventionlayer may have at least one selected from a magnetic element and anelement having an atomic number equal to or higher than that of yttrium.

(5) In the spin current magnetization rotational magnetoresistanceeffect element according to the above aspect, a thickness of thediffusion prevention layer may be equal to or less than four times anatomic radius of an atom constituting the diffusion prevention layer.

(6) In the spin current magnetization rotational magnetoresistanceeffect element according to the above aspect, the spin-orbit torquewiring may include a nonmagnetic metal having an atomic number of 39 orhigher having a d electron or an f electron in an outermost shell.

(7) In the spin current magnetization rotational magnetoresistanceeffect element according to the above aspect, the spin-orbit torquewiring may be formed of a pure spin current generation part made of amaterial that generates a pure spin current, and a low resistance partmade of a material having electric resistance lower than electricalresistance of the pure spin current generation part, and at least a partof the pure spin current generation part may be in contact with the caplayer.

(8) A magnetic memory according to a third aspect includes the spincurrent magnetization rotational magnetoresistance effect elementdescribed above.

(9) A method of manufacturing a spin current magnetization rotationalmagnetoresistance effect element including the steps of: forming alaminate in which a first ferromagnetic metal layer in which a directionof magnetization is fixed, a nonmagnetic layer, a second ferromagneticmetal layer configured for a direction of magnetization to be changed, acap layer, and a process protection layer are laminated in an order on asubstrate; processing the laminate into a predetermined shape to form amagnetoresistance effect element; and removing the process protectionlayer and forming a spin-orbit torque wiring on an exposed surfaceexposed after the removal.

Advantageous Effects of Invention

According to the spin current magnetization rotational magnetoresistanceeffect element according to the above aspects, a spin-orbit torque (SOT)induced by a pure spin current can be efficiently utilized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically illustrating a spin currentmagnetization rotational magnetoresistance effect element according to afirst embodiment.

FIG. 2 is a schematic view for describing a spin Hall effect.

FIG. 3 is a schematic view for describing one embodiment of a spin-orbittorque wiring, in which (a) is a cross-sectional view and (b) is a planview.

FIG. 4 is a schematic view for describing another embodiment of thespin-orbit torque wiring, in which (a) is a cross-sectional view and (b)is a plan view.

FIG. 5 is a schematic view for describing another embodiment of thespin-orbit torque wiring, in which (a) is a cross-sectional view and (b)is a plan view.

FIG. 6 is a schematic view for describing another embodiment of thespin-orbit torque wiring, in which (a) is a cross-sectional view and (b)is a plan view.

FIG. 7 is a perspective view schematically illustrating a spin currentmagnetization rotational magnetoresistance effect element according to asecond embodiment.

FIG. 8 is a view illustrating a manufacturing method of a spin currentmagnetization rotational magnetoresistance effect element according tothe present embodiment.

FIG. 9 is a schematic cross-sectional view of the spin currentmagnetization rotational magnetoresistance effect element according tothe present embodiment taken along an xz plane.

FIG. 10 is a schematic cross-sectional view of another example of thespin current magnetization rotational magnetoresistance effect elementaccording to the present embodiment taken along the xz plane.

FIG. 11 is a perspective view schematically illustrating the spincurrent magnetization rotational magnetoresistance effect elementaccording to the present embodiment including a power supply.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present embodiment will be described in detail withreference to the drawings as appropriate. In the drawings used in thefollowing description, there are cases in which characteristic portionsare appropriately enlarged for convenience of illustration so thatcharacteristics of the present disclosure can be easily understood, anddimensional ratios of respective constituent elements may be differentfrom actual ones. Materials, dimensions, and the like illustrated in thefollowing description are merely examples, and the present disclosure isnot limited thereto but can be implemented with appropriatemodifications within the range in which the effect of the presentdisclosure is achieved.

(Spin Current Magnetization Rotational Magnetoresistance Effect Element)

First Embodiment

FIG. 1 is a perspective view schematically illustrating a spin currentmagnetization rotational magnetoresistance effect element according to afirst embodiment.

As illustrated in FIG. 1, the spin current magnetization rotationalmagnetoresistance effect element 100 includes a substrate 10, amagnetoresistance effect element 20, and a spin-orbit torque wiring 40.In FIG. 1, a wiring 30 for causing a current to flow in a laminationdirection of the magnetoresistance effect element 20 is alsoillustrated. The spin-orbit torque wiring 40 is joined to themagnetoresistance effect element 20 and extends in a directionintersecting the lamination direction of the magnetoresistance effectelement 20.

Hereinafter, as an example of a configuration in which the spin-orbittorque wiring extends in a direction intersecting the laminationdirection of the magnetoresistance effect element, a case of aconfiguration in which the spin-orbit torque wiring extends in adirection perpendicular to the lamination direction of themagnetoresistance effect element will be described.

Hereinafter, the lamination direction of the magnetoresistance effectelement 20 is a z direction, a direction thereof perpendicular to the zdirection and parallel to the spin-orbit torque wiring 40 is an xdirection, and a direction thereof perpendicular to the x direction andz direction is a y direction.

<Substrate>

The substrate 10 is preferably excellent in flatness. In order to obtaina surface excellent in flatness, for example, a semiconductor such asSi, Ge, GaAs, or InGaAs, or AlTiC or the like can be used as a material.Further, the substrate 10 may have a circuit on a material such as asemiconductor such as Si, Ge, GaAs, or InGaAs, or AlTiC or the like.

<Magnetoresistance Effect Element>

The magnetoresistance effect element 20 includes a first ferromagneticmetal layer 21, a nonmagnetic layer 22, a second ferromagnetic metallayer 23, and a cap layer 24 in that order from the substrate 10 side.

Magnetization of the first ferromagnetic metal layer 21 is fixed in onedirection and a direction of magnetization of the second ferromagneticmetal layer 23 changes relative to the magnetization of the firstferromagnetic metal layer 21 to function as the magnetoresistance effectelement 20. When it is applied to a coercivity-differed type (pseudospin valve type) magnetic random access memory (MRAM), coercivity of thefirst ferromagnetic metal layer 21 is larger than coercivity of thesecond ferromagnetic metal layer 23. In addition, when it is applied toan exchange bias type (spin valve type) MRAM, a direction ofmagnetization of the first ferromagnetic metal layer 21 is fixed byexchange coupling with an antiferromagnetic layer.

When the nonmagnetic layer 22 is formed of an insulator, themagnetoresistance effect element 20 is a tunneling magnetoresistance(TMR) element, and when the nonmagnetic layer 22 is formed of a metal,the magnetoresistance effect element 20 is a giant magnetoresistance(GMR) element.

For the magnetoresistance effect element according to the embodiment, aconfiguration of a known magnetoresistance effect element can beemployed. For example, each layer may be formed of a plurality oflayers, or another layer such as an antiferromagnetic layer for fixing adirection of magnetization of the first ferromagnetic metal layer may beprovided. The first ferromagnetic metal layer 21 is called a fixedlayer, a reference layer, or the like, and the second ferromagneticmetal layer 23 is called a free layer, a storage layer, or the like.

The first ferromagnetic metal layer 21 is disposed on the substrate 10side with respect to the second ferromagnetic metal layer 23. When thefirst ferromagnetic metal layer 21 serving as a fixed layer is disposedon the substrate 10 side, magnetization of the first ferromagnetic metallayer 21 is stabilized. When the magnetization of the firstferromagnetic metal layer 21 is stabilized, fluctuation of background ofa magnetoresistance (MR) ratio is inhibited, and noise of themagnetoresistance effect element 20 is reduced.

The first ferromagnetic metal layer 21 and the second ferromagneticmetal layer 23 may be either an in-plane magnetization film of which amagnetization direction is an in-plane direction parallel to the layeror a perpendicular magnetization film of which a magnetization directionis a direction perpendicular to the layer.

As a material of the first ferromagnetic metal layer 21, a knownmaterial can be used. For example, a metal selected from the groupconsisting of Cr, Mn, Co, Fe and Ni, and an alloy containing one or moreof these metals and exhibiting ferromagnetism can be used. It is alsopossible to use an alloy containing these metals and at least one of theelements B, C, and N. Specifically, Co—Fe or Co—Fe—B can be exemplified.

In order to obtain a higher output, it is preferable to use a Heusleralloy such as Co₂FeSi as a material of the first ferromagnetic metallayer 21. A Heusler alloy contains an intermetallic compound having achemical composition of X₂YZ, and X indicates a transition metal elementof Co, Fe, Ni, or Cu group, or a noble metal element in the periodictable. Y indicates a transition metal of Mn, V, Cr, or Ti group, and canalso be elemental species of X. Z indicates a typical element from GroupIII to Group V. Co₂FeSi, Co₂MnSi, Co₂Mn_(1-a)Fe_(a)Al_(b)Si_(1-b), andthe like can be exemplified as a Heusler alloy.

An antiferromagnetic material such as IrMn, PtMn or the like may bebrought into contact with a surface of the first ferromagnetic metallayer 21 opposite to the second ferromagnetic metal layer 23. Coercivityof the first ferromagnetic metal layer 21 with respect to the secondferromagnetic metal layer 23 can be further increased. Further, themagnetoresistance effect element 20 may have a synthetic ferromagneticcoupling structure to prevent a leakage magnetic field of the firstferromagnetic metal layer 21 from affecting the second ferromagneticmetal layer 23.

When a direction of magnetization of the first ferromagnetic metal layer21 is made perpendicular to a lamination surface, it is preferable touse a film in which Co and Pt are laminated. Specifically, the firstferromagnetic metal layer 21 is formed of [Co (0.24 nm)/Pt (0.16nm)]₆/Ru (0.9 nm)/[Pt (0.16 nm)/Co (0.16 nm)]₄/T (0.2 nm)/FeB (1.0 nm).

As the second ferromagnetic metal layer 23, a ferromagnetic material,particularly a soft magnetic material, can be applied. For example, ametal selected from the group consisting of Cr, Mn, Co, Fe and Ni, analloy containing one or more of these metals, and an alloy containingthese metals and at least one of the elements B, C, and N, or the likecan be used. Specifically, Co—Fe, Co—Fe—B, Ni—Fe can be exemplified.

When a direction of magnetization of the second ferromagnetic metallayer 23 is made perpendicular to the lamination surface, a thickness ofthe second ferromagnetic metal layer is preferably 2.5 nm or less.Perpendicular magnetic anisotropy can be added to the secondferromagnetic metal layer 23 at an interface between the secondferromagnetic metal layer 23 and the nonmagnetic layer 22. A filmthickness of the second ferromagnetic metal layer 23 is preferablysmall. An effect of the perpendicular magnetic anisotropy is attenuatedwhen the film thicknesses of the second ferromagnetic metal layer 23increases.

For the nonmagnetic layer 22, a known material can be used.

For example, when the nonmagnetic layer 22 is formed of an insulator (inthe case of a tunnel barrier layer), Al₂O₃, SiO₂, Mg, MgAl₂O₄O, or thelike can be used as the material. In addition to these materials, amaterial in which a part of Al, Si, and Mg is substituted with Zn, Be orthe like can also be used as the tunnel barrier layer. Of these, MgO andMgAl₂O₄ are materials that can realize coherent tunneling, and spin canbe efficiently injected into the second ferromagnetic metal layer 23.

When the nonmagnetic layer 22 is formed of a metal, Cu, Au, Ag, or thelike can be used as the material.

The cap layer 24 is a layer connecting the second ferromagnetic metallayer 23 to the spin-orbit torque wiring 40. Although details will bedescribed in a manufacturing method to be described below, the cap layer24 is a layer that can be polished during a manufacturing process.Therefore, when the cap layer 24 is provided on the second ferromagneticmetal layer 23, a surface on which the spin-orbit torque wiring 40 islaminated can be planarized.

A spin-orbit torque (SOT) accompanying a pure spin current is greatlyaffected by an interface of the lamination surface. When the interfacebetween the cap layer 24 and the spin-orbit torque wiring 40 isplanarized, a pure spin current can be efficiently supplied to thesecond ferromagnetic metal layer 23, and a large SOT can be obtained.

On the other hand, the pure spin current generated in the spin-orbittorque wiring 40 passes through the cap layer 24 before reaching thesecond ferromagnetic metal layer 23. Although the cap layer 24 is alayer needed for planarizing the interface, when the spin passingthrough the cap layer 24 is diffused, a sufficient pure spin currentcannot be supplied to the second ferromagnetic metal layer 23.

Therefore, the cap layer 24 preferably does not easily dissipate thespin transferred from the spin-orbit torque wiring 40. That is, the caplayer 24 is required to have spin conductivity, and it is preferable tomainly have a substance having high spin conductivity.

Copper, silver, magnesium, aluminum, silicon, germanium, galliumarsenide, and the like have long spin diffusion lengths of 100 nm ormore even at room temperature, and do not easily dissipate spin.Therefore, it is preferable that the cap layer 24 mainly has one or moreelements selected from the group consisting of these materials.

A thickness of the cap layer 24 is preferably equal to or less than thespin diffusion length of the substance forming the cap layer 24. Whenthe thickness of the cap layer 24 is equal to or less than the spindiffusion length, the spin transferred from the spin-orbit torque wiring40 can be sufficiently transferred to the magnetoresistance effectelement 20.

Further, the cap layer 24 also contributes to a crystal orientation ofeach layer of the magnetoresistance effect element 20. The cap layer 24stabilizes magnetism of the first ferromagnetic metal layer 21 and thesecond ferromagnetic metal layer 23 of the magnetoresistance effectelement 20, and contributes to low resistance of the magnetoresistanceeffect element 20.

<Spin-Orbit Torque Wiring>

The spin-orbit torque wiring 40 extends in a direction intersecting thelamination direction of the magnetoresistance effect element 20. A powersupply for causing a current to flow along the spin-orbit torque wiring40 is electrically connected to the spin-orbit torque wiring 40. Thespin-orbit torque wiring 40 and the power supply function as spininjection means for injecting a pure spin current into themagnetoresistance effect element.

The spin-orbit torque wiring 40 is made of a material in which a purespin current is generated by a spin Hall effect when a current flows. Assuch a material, any material may be sufficient as long as it has aconfiguration in which a pure spin current is generated in thespin-orbit torque wiring 40. Therefore, it is not limited to a materialformed of a single element, but a material formed of a part configuredwith a material from which a pure spin current is generated and a partconfigured with a material from which no pure spin current is generated,or the like may be used.

The spin Hall effect is a phenomenon in which a pure spin current isinduced in a direction perpendicular to a current direction on the basisof spin-orbit interaction when a current flows in a material.

FIG. 2 is a schematic view for describing a spin Hall effect. Amechanism in which a pure spin current is generated by the spin Halleffect will be described with reference to FIG. 2.

As illustrated in FIG. 2, when a current I flows in an extendingdirection of the spin-orbit torque wiring 40, a first spin S1 and asecond spin S2 are respectively bent in a direction perpendicular to thecurrent. A normal Hall effect and a spin Hall effect are common in thatmotion (movement) of electric charges (electrons) is bent in a motion(movement) direction. On the other hand, while charged particles movingin a magnetic field are subjected to a Lorentz force and a direction ofthe motion is bent in the normal Hall effect, the spin Hall effect isgreatly different in that, even though there is no magnetic field, whenelectrons merely move (when a current merely flows), a moving directionthereof is bent.

Since the number of electrons of the first spin S1 is equal to thenumber of electrons of the second spin S2 in a nonmagnetic material (amaterial which is not a ferromagnetic material), the number of electronsof the first spin Si directed upward and the number of electrons of thesecond spin S2 directed downward in the drawing are the same. Therefore,the current as a net flow of electric charges is zero. This spin currentthat does not accompany a current is particularly called a pure spincurrent.

On the other hand, also when a current flows through a ferromagneticmaterial, it is the same point in that first spin electrons and secondspin electrons are bent in opposite directions from each other. However,since a ferromagnetic material is in a state in which either the firstspin electrons or the second spin electrons are more than the other, asa result, a net flow of electric charges occurs (a voltage isgenerated). Therefore, as a material of the spin-orbit torque wiring, amaterial formed of only a ferromagnetic material is not included.

Here, when a flow of electrons in the first spin S1 is expressed asJ_(⬆), a flow of electrons in the second spin S2 is expressed as J_(⬇),and a spin current is expressed as J_(s), it is defined byJ_(s)=J_(⬆)−J_(⬇). In FIG. 2, the pure spin current J_(s) flows upwardin the drawing. Here, J_(s) is a flow of electrons with a polarizabilityof 100%.

In FIG. 2, when a ferromagnetic material is brought into contact with anupper surface of the spin-orbit torque wiring 40, the pure spin currentdiffuses and flows into the ferromagnetic material. In the presentembodiment, the pure spin current generated by causing a current to flowthrough the spin-orbit torque wiring 40 diffuses into the secondferromagnetic metal layer 23 via the cap layer 24. The magnetization ofthe second ferromagnetic metal layer 23 serving as a free layer isrotated in magnetization due to the spin-orbit torque (SOT) effect bythe pure spin current.

Magnetization rotation is not necessarily performed using only the SOTeffect. For example, magnetization rotation may be performed using aspin transfer torque (STT) effect together with the SOT. In addition, anexternal magnetic field, heat, a voltage, lattice distortion, or thelike may be used together with the SOT.

The spin-orbit torque wiring 40 may include a nonmagnetic heavy metal.Here, “heavy metal” is used to mean a metal having a specific gravityequal to or higher than that of yttrium. The spin-orbit torque wiring 40may be formed of only a nonmagnetic heavy metal.

In this case, the nonmagnetic heavy metal is preferably a nonmagneticmetal having a high atomic number such as the atomic number of 39 orhigher having a d electron or an f electron in an outermost shell.Nonmagnetic metals have a large spin-orbit interaction which causes aspin Hall effect. The spin-orbit torque wiring 40 may be formed of onlya nonmagnetic metal having a high atomic number such as the atomicnumber of 39 or higher having a d electron or an f electron in anoutermost shell.

Normally, when a current flows in a metal, all of the electrons move ina direction opposite to the current regardless of a direction of theirspin. In contrast, since the nonmagnetic metal with a high electronnumber having d electrons and f electrons in an outermost shell has alarge spin-orbit interaction, a movement direction of electrons dependson a spin direction of electrons due to the spin Hall effect and thepure spin current J_(s) is easily generated.

The spin-orbit torque wiring 40 may include a magnetic metal. Themagnetic metal indicates a ferromagnetic metal or an antiferromagneticmetal. When a very small amount of magnetic metal is contained in anonmagnetic metal, the spin-orbit interaction is enhanced and spincurrent generation efficiency with respect to a current flowing throughthe spin-orbit torque wiring 40 increases. The spin-orbit torque wiring40 may be formed of only an antiferromagnetic metal.

Since spin-orbit interaction is caused by an inherent inner space of asubstance of the spin-orbit torque wiring material, a pure spin currentis generated even in a nonmagnetic material. When a very small amount ofa magnetic metal is added to the spin-orbit torque wiring material, themagnetic metal itself scatters electron spins flowing therethrough andthe spin current generation efficiency increases.

However, when an additive amount of the magnetic metal is excessivelyincreased, the generated pure spin current is scattered by the addedmagnetic metal, and as a result, an effect of decreasing the spincurrent increases. Therefore, a molar ratio of the added magnetic metalis preferably sufficiently smaller than a molar ratio of a majorcomponent of a pure spin generation part in the spin-orbit torquewiring. As a reference, the molar ratio of the added magnetic metal ispreferably 3% or less.

The spin-orbit torque wiring 40 may include a topological insulator. Thespin-orbit torque wiring 40 may be formed of only the topologicalinsulator. The topological insulator is a material in which the interiorof the substance is an insulator or a highly resistive material while aspin-polarized metallic state is generated on a surface thereof.

In a substance, there is something like an internal magnetic fieldcalled spin-orbit interaction. Due to an effect of this spin-orbitinteraction, a new topological phase is exhibited even without anexternal magnetic field. This is the topological insulator and it cangenerate the pure spin current with high efficiency by strong spin-orbitinteraction and breaking of rotation symmetry at an edge.

As the topological insulator, for example, SnTe,Bi_(1.5)Sb_(0.5)Te_(1.7)Se_(1.3), TlBiSe₂, Bi₂Te₃, (Bi_(1-x)Sb_(x))₂Te₃,and the like are preferable. These topological insulators can generatethe spin current with high efficiency.

FIGS. 3 to 6 are schematic views for describing embodiments of thespin-orbit torque wiring, in which (a) is a cross-sectional view and (b)is a plan view.

A heavy metal, which is a material capable of generating a pure spincurrent, has higher electric resistance as compared with a metal usedfor an ordinary wiring. Therefore, in view of reducing Joule heat, it ispreferable that the spin-orbit torque wiring 40 include a part with lowelectric resistance, rather than the entire spin-orbit torque wiring 40being made of a material capable of generating the pure spin current.That is, it is preferable that the spin-orbit torque wiring 40 be formedof a part (spin current generation part) made of a material thatgenerates a pure spin current and a part (low resistance part) made of amaterial having a lower electric resistance than the spin currentgeneration part.

The spin current generation part may be made of a material capable ofgenerating a pure spin current, and may have, for example, aconfiguration constituted by a plurality of types of material parts, orthe like.

For the low resistance part, a material used for a normal wiring can beused. For example, aluminum, silver, copper, gold, or the like can beused. The low resistance part may be made of a material having lowerelectric resistance than the spin current generation part, and may have,for example, a configuration constituted by a plurality of types ofmaterial parts, or the like.

Further, the low resistance part is not limited to one that does notgenerate a pure spin current, and one generating a pure spin current mayalso be used. In this case, in regard to distinction between the spincurrent generation part and the low resistance part, the parts formed ofthe materials described as the materials of the spin current generationpart and the low resistance part in this specification can bedistinguished as being the spin current generation part or the lowresistance part. In addition, a part other than a main part generatingthe pure spin current and having a lower electric resistance than themain part is the low resistance part and can be distinguished from thespin current generation part.

The spin current generation part may include a nonmagnetic heavy metal.A heavy metal capable of producing a pure spin current may be includedin a finite amount. A material composition of the spin currentgeneration part is preferably one of the following two. One is a case inwhich a major component of the spin current generation part is occupiedby a heavy metal capable of generating a pure spin current, and anotheris a case in which a heavy metal capable of generating a pure spincurrent occupies a sufficiently smaller concentration region than thatof a major component of the spin current generation part.

When the major component of the spin current generation part is occupiedby the heavy metal capable of generating a pure spin current, a ratiothereof is preferably 90% or more, or is preferably 100%. The heavymetal in this case is a nonmagnetic metal having an atomic number of 39or higher having a d electron or an f electron in an outermost shell.

On the other hand, as an example of a case in which a concentrationoccupied by the heavy metal capable of generating a pure spin current ismuch smaller than that of the major component of the spin currentgeneration part, a case in which the major component of the spin currentgeneration part is copper and the heavy metal is contained at aconcentration of 10% or less in terms of molar ratio can be exemplified.

As described above, when the heavy metal capable of generating a purespin current occupies a sufficiently smaller concentration region thanthat of the major component of the spin current generation part, aconcentration of the heavy metal contained in the spin currentgeneration part is preferably 50% or less, more preferably 10% or less,in terms of molar ratio. When a concentration range of the heavy metalis within the above range, a spin scattering effect by electrons can beeffectively obtained.

Here, when the heavy metal capable of a generating pure spin currentoccupies a sufficiently smaller concentration region than that of themajor component of the spin current generation part, the major componentconstituting the spin current generation part is formed of one otherthan the above-described heavy metals. In other words, a main partconstituting the spin current generation part is a light metal having anatomic number smaller than that of the heavy metal, and the other partis the heavy metal.

An assumption here is that the heavy metal and the light metal do notform an alloy, but atoms of the heavy metal are randomly dispersed inthe light metal. Spin-orbit interaction is weak in a light metal and apure spin current due to the spin Hall effect cannot easily be generatedin the light metal which is the major component. However, when a heavymetal is contained in the light metal, spins are scattered at aninterface between the light metal and the heavy metal when electronspass through the heavy metal in the light metal. As a result, it ispossible to efficiently generate the pure spin current even when aconcentration of the heavy metal is low.

On the other hand, when a concentration of the heavy metal exceeds 50%,although a ratio of the spin Hall effect in the heavy metal increases,the effect at the interface between the light metal and the heavy metaldecreases, and thus the effect decreases as a whole. Therefore, aconcentration of the heavy metal to such an extent that a sufficientinterface effect can be expected is preferable.

In addition, the spin current generation part can be formed of anantiferromagnetic metal. This is an example of a case in which thespin-orbit torque wiring 40 described above includes a magnetic metal.When the spin current generation part is formed of an antiferromagneticmetal, it is possible to obtain the same effect as in a case in whichthe nonmagnetic heavy metal with an atomic number 39 or more having a delectron or an f electron in an outermost shell is 100%. Theantiferromagnetic metal is, for example, preferably IrMn or PtMn, andIrMn that is stable to heat is more preferable.

In addition, the spin current generation part can be formed of atopological insulator. This is an example of a case in which thespin-orbit torque wiring described above includes a topologicalinsulator. As the topological insulator, for example, SnTe,Bi_(1.5)Sb_(0.5)Te_(1.7)Se_(1.3), TlBiSe₂, Bi₂Te₃, (Bi_(1-x)Sb_(x))₂Te₃and the like are preferable. These topological insulators can generate aspin current with high efficiency.

In order for the pure spin current generated in the spin-orbit torquewiring to effectively diffuse into the magnetoresistance effect element,at least a part of the spin current generation part needs to be incontact with the magnetoresistance effect element 20. All of theembodiments of the spin-orbit torque wiring illustrated in FIGS. 3 to 6have a configuration in which the spin current generation part is incontact with the cap layer 24 at least in part.

In the spin-orbit torque wiring 40 illustrated in FIG. 3, an entirejunction 40′ with the cap layer 24 is formed of the spin currentgeneration part 41, and the spin current generation part 41 issandwiched between low resistance parts 42A and 42B.

Here, when the spin current generation part and the low resistance partare disposed electrically in parallel, a current flowing through thespin-orbit torque wiring is divided into proportions of an inverse ratioof magnitudes of resistances of the spin current generation part and thelow resistance part, and thereby flows through respective parts.

In view of pure spin current generation efficiency, it is preferablethat all the current flowing through the spin-orbit torque wiring flowthrough the spin current generation part. In other words, it ispreferable that there be no part in which the spin current generationpart and the low resistance part are electrically disposed in parallel,and that all be electrically disposed in series.

The spin-orbit torque wirings illustrated in FIGS. 3 to 6 haveconfigurations in which there is no part of the spin current generationpart and the low resistance part that is electrically disposed inparallel in a plan view from the lamination direction of themagnetoresistance effect element. These configurations can increase thepure spin current generation efficiency.

In the spin-orbit torque wiring 40 illustrated in FIG. 3, the spincurrent generation part 41 is superimposed on a junction 24′ with thecap layer 24 to include the junction 24′ in a plan view from thelamination direction of the magnetoresistance effect element 20. Athickness direction of the spin-orbit torque wiring 40 is formed of onlythe spin current generation part 41, and the low resistance parts 42Aand 42B sandwich the spin current generation part 41 in a direction ofcurrent flow. As a modified example of the spin-orbit torque wiringillustrated in FIG. 3, there are cases in which the spin currentgeneration part 41 is superimposed on the junction 24′ of the cap layer24 so that the junction 24′ is overlaid with the spin current generationpart 41 in a plan view from the lamination direction of themagnetoresistance effect element 20. In this modified example,configurations other than this part are the same as the spin-orbittorque wiring illustrated in FIG. 3.

In the spin-orbit torque wiring 40 illustrated in FIG. 4, the spincurrent generation part 41 is superimposed on a part of the junction 24′of the cap layer 24 in a plan view from the lamination direction of themagnetoresistance effect element 20. The thickness direction of thespin-orbit torque wiring 40 is formed of only the spin currentgeneration part 41, and the low resistance parts 42A and 42B sandwichthe spin current generation part 41 in a direction of current flow.

In the spin-orbit torque wiring 40 illustrated in FIG. 5, the spincurrent generation part 41 is superimposed on the junction 24′ of thecap layer 24 to include the junction 24′ in a plan view from thelamination direction of the magnetoresistance effect element 20. In thethickness direction of the spin-orbit torque wiring 40, the spin currentgeneration part 41 and a low resistance part 42C are laminated in orderfrom the magnetoresistance effect element 20 side. A part in which thespin current generation part 41 and the low resistance part 42C arelaminated is sandwiched between the low resistance parts 42A and 42B ina direction of current flow. As a modified example of the spin-orbittorque wiring illustrated in FIG. 5, there are cases in which the spincurrent generation part 41 is superimposed on the junction 24′ of thecap layer 24 so that the junction 24′ is overlaid with the spin currentgeneration part 41 in a plan view from the lamination direction of themagnetoresistance effect element 20. In this modified example,configurations other than this part are the same as the spin-orbittorque wiring illustrated in FIG. 5.

In the spin-orbit torque wiring 40 illustrated in FIG. 6, the spincurrent generation part 41 includes a first spin current generation part41A and a second spin current generation part 41B. The first spincurrent generation part 41A is a part formed on an entire surface of thespin current generation part 41 on the magnetoresistance effect element20 side. The second spin current generation part 41B is a part laminatedon the first spin current generation part 41A and is a part superimposedon the junction 24′ of the cap layer 24 to include the junction 24′ in aplan view from the lamination direction of the magnetoresistance effectelement 20. The second spin current generation part 41B is sandwichedbetween the low resistance parts 42A and 42B in a direction of currentflow.

As a modified example of the spin-orbit torque wiring illustrated inFIG. 6, there are cases in which the second spin current generation part41B is superimposed on the junction 24′ of the cap layer 24 so that thejunction 24′ is overlaid with the second spin current generation part41B in a plan view from the lamination direction of themagnetoresistance effect element 20. In this modified example,configurations other than this part are the same as the spin-orbittorque wiring illustrated in FIG. 6. In the configuration illustrated inFIG. 6, since an area of contact between the spin current generationpart 41 and the low resistance part 42 is wide, the adhesion between thespin current generation part 41 and the low resistance part 42 is high.

In FIGS. 3 to 6, a thickness and a width in a y direction of thespin-orbit torque wiring 40 are illustrated to be constant in adirection of current flow. However, a shape of the spin-orbit torquewiring 40 is not limited to this configuration. For example, thespin-orbit torque wiring 40 may be narrowed in a part superimposed onthe magnetoresistance effect element 20 in a plan view from thelamination direction. A current flowing through the spin-orbit torquewiring 40 is concentrated at the narrowed part. In other words, currentefficiency supplied to the spin current generation part 41 is increasedand generation efficiency of the pure spin current can be increased.

In FIGS. 3 to 6, a width of the spin current generation part 41 in an xdirection (a direction of current flow) is constant in principle in athickness direction of the spin-orbit torque wiring 40. However, a shapeof the spin current generation part 41 is not limited to thisconfiguration. For example, the width of the spin current generationpart 41 in the x direction may be configured to decrease in diametertoward the magnetoresistance effect element 20. The spin currentgeneration part 41 has a larger resistance than the low resistance parts42A and 42B. Therefore, a part of the current flowing through thespin-orbit torque wiring 40 flows along interfaces between the spincurrent generation part 41 and the low resistance parts 42A and 42B. Asa result, a large amount of current can be supplied to the interfacebetween the magnetoresistance effect element 20 and the spin-orbittorque wiring 40, and supply efficiency of the pure spin current to thesecond ferromagnetic metal layer 23 can be further enhanced.

<Underlayer>

An underlayer (not illustrated) may be formed on a surface of thesubstrate 10 on the magnetoresistance effect element 20 side. When theunderlayer is provided, it is possible to control crystalline propertiesof each layer including the first ferromagnetic metal layer 21 laminatedon the substrate 10 such as crystal orientation, crystal grain size, orthe like.

The underlayer preferably has insulation properties. This is to preventdissipation of a current flowing through the wiring 30 or the like.Various materials can be used for the underlayer.

For example, as one example, a nitride layer having a (001)-orientedNaCl structure and containing at least one element selected from thegroup consisting of Ti, Zr, Nb, V, Hf, Ta, Mo, W, B, Al, and Ce can beused for the underlayer.

As another example, a layer of a (002)-oriented perovskite-basedconductive oxide expressed by a composition formula of ABO₃ can be usedfor the underlayer. Here, a site A contains at least one elementselected from the group consisting of Sr, Ce, Dy, La, K, Ca, Na, Pb, andBa, and a site B contains at least one element selected from the groupconsisting of Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Nb, Mo, Ru, Ir, Ta, Ce, andPb.

As another example, an oxide layer having a (001)-oriented NaClstructure and containing at least one element selected from the groupconsisting of Mg, Al, and Ce can be used for the underlayer.

As another example, a layer having a (001)-oriented crystal structure ora cubic crystal structure and containing at least one element selectedfrom the group consisting of Al, Cr, Fe, Co, Rh, Pd, Ag, Ir, Pt, Au, Mo,and W can be used for the underlayer.

The underlayer is not limited to one layer, and may have a plurality oflayers in which the above-described examples are laminated. By devisinga structure of the underlayer, crystalline properties of each layer ofthe magnetoresistance effect element 20 can be enhanced, and magneticcharacteristics can be improved.

<Wiring>

The wiring 30 is electrically connected to the first ferromagnetic metallayer 21 of the magnetoresistance effect element 20. In a case in whichmagnetization of the second ferromagnetic metal layer 23 is rotatedusing only an SOT, the wiring 30 is unnecessary. On the other hand, whenan STT is utilized in addition to the SOT, it is necessary to cause acurrent to flow in the lamination direction of the magnetoresistanceeffect element 20, and thus the wiring 30 is necessary.

The wiring 30 is not particularly limited as long as it is a highlyconductive material. For example, aluminum, silver, copper, gold, or thelike can be used.

Second Embodiment

FIG. 7 is a schematic perspective view of a spin current magnetizationrotational magnetoresistance effect element according to a secondembodiment. A spin current magnetization rotational magnetoresistanceeffect element 101 according to the second embodiment is different fromthe spin current magnetization rotational magnetoresistance effectelement 100 according to the first embodiment in that a diffusionprevention layer 26 is provided. Other configurations are the same asthose of the spin current magnetization rotational magnetoresistanceeffect element 100 according to the first embodiment, and are denoted bythe same reference signs.

The spin current magnetization rotational magnetoresistance effectelement 101 according to the second embodiment includes amagnetoresistance effect element 25 and a spin-orbit torque wiring 40.The magnetoresistance effect element 25 includes a diffusion preventionlayer 26 between a second ferromagnetic metal layer 23 and a cap layer24. When the diffusion prevention layer 26 is provided, the spin-orbittorque wiring 40 may be provided on a substrate 10 side.

The diffusion prevention layer 26 is a layer for preventing elementsforming the cap layer 24 from diffusing into the second ferromagneticmetal layer 23. As described above, the cap layer 24 is required to havespin conductivity so that a pure spin current supplied from thespin-orbit torque wiring 40 to the second ferromagnetic metal layer 23is not diffused. However, when only this point is considered, there arecases in which a light element is used as an element forming the caplayer 24 and this element diffuses into the second ferromagnetic metallayer 23.

When a nonmagnetic element diffuses into the second ferromagnetic metallayer 23, a magnetization characteristic of the second ferromagneticmetal layer 23 deteriorates. For example, Mg is an element that can beused for the cap layer 24, but is an element that easily diffuses. Byproviding the diffusion prevention layer 26 between the cap layer 24 andthe second ferromagnetic metal layer 23, diffusion of atoms from the caplayer 24 to the second ferromagnetic metal layer 23 is prevented.

The diffusion prevention layer 26 preferably has at least one selectedfrom a magnetic element and an element having an atomic number equal toor higher than that of yttrium. These elements are heavy and do noteasily move. That is, these elements inhibit inflow of diffusingelements. That is, diffusion of the element forming the cap layer 24into the second ferromagnetic metal layer 23 is inhibited. Further,since these elements are heavy, the element itself forming the diffusionprevention layer 26 cannot easily diffuse into the second ferromagneticmetal layer 23.

Also, a part of the current flowing through the spin-orbit torque wiring40 is also supplied to the diffusion prevention layer 26. Therefore, forexample, when a material constituting the diffusion prevention layer 26is a nonmagnetic heavy metal, a pure spin current can be generated alsoin the diffusion prevention layer 26.

A thickness of the diffusion prevention layer 26 is preferably equal toor less than four times an atomic radius (twice the atomic diameter) ofthe atom constituting the diffusion prevention layer and is morepreferably less than twice the atomic radius (equal to the atomicdiameter). Here, the thickness of the diffusion prevention layer 26 is athickness laminated in calculation at the time of manufacturing.

In view of preventing elements from diffusing, the diffusion preventionlayer 26 preferably forms a dense layer. However, when a dense layer isformed, a magnetic correlation may also be blocked. Therefore, in orderto prevent elements from diffusing while a magnetic correlation ismaintained, it is most preferable that elements forming the diffusionprevention layer 26 be present dissipatively in a plane of the layer.

When the thickness in calculation at the time of laminating thediffusion prevention layer 26 is equal to or less than four times theatomic radius of the atom (twice the atomic diameter), a dense layer isnot formed and a gap is formed unless precise control is performed.Also, when it is less than twice the atomic radius of the atom (equal tothe atomic diameter), it is clear that it is less than a thickness ofone atom layer and a dense layer is not formed.

Although the diffusion prevention layer 26 is a very thin layer asdescribed above, it can be analyzed using energy dispersive X-rayspectroscopy (EDS). Further, the thickness of the diffusion preventionlayer 26 can also be estimated from a spatial resolution of an apparatusand a half-value width of an obtained peak.

(Method of Manufacturing Spin Current Magnetization RotationalMagnetoresistance Effect Element)

Next, a method of manufacturing a spin current magnetization rotationalmagnetoresistance effect element according to the present embodimentwill be described. FIG. 8 is a view schematically illustrating amanufacturing method of a spin current magnetization rotationalmagnetoresistance effect element according to the present embodiment.

Hereinafter, a case in which a diffusion prevention layer is notprovided will be described as an example. In a case in which a diffusionprevention layer is provided, only a process of laminating the diffusionprevention layer between the second ferromagnetic metal layer 23 and thecap layer 24 is added, and the other processes are the same.

First, as illustrated in FIG. 8 (a), a wiring metal layer 31, a firstferromagnetic metal layer 21, a nonmagnetic layer 22, the secondferromagnetic metal layer 23, the cap layer 24, and a process protectionlayer 27 are laminated in that order on the substrate 10. Whenmagnetization rotation is performed using only a spin-orbit torque(SOT), the wiring metal layer 31 is unnecessary.

As a method of laminating these, a known method can be used. Forexample, a sputtering method, an evaporation method, a laser ablationmethod, a molecular beam epitaxy (MBE) method, or the like can be used.For the nonmagnetic layer 22, a metal thin film may be sputtered and anobtained sputtered metal thin film may be subjected to plasma oxidationor natural oxidation by introducing oxygen.

The process protection layer 27 is a layer that is removed duringprocessing and is a layer that prevents processing damage from beingapplied to the second ferromagnetic metal layer 23. The processprotection layer 27 may be formed using the same material as the caplayer 24 or using a different material.

The process protection layer 27 is preferably not selectively etchedduring the processing and preferably has mechanical hardness. Therefore,it is preferable to use at least one element selected from the groupconsisting of Ru, Ta, SiN, W, and Mo as a material constituting theprocess protection layer 27.

Next, as illustrated in FIG. 8 (b), a resist or the like is provided onthe process protection layer 27, a laminate is processed into apredetermined shape, and the magnetoresistance effect element 20 ismanufactured. When the wiring 30 and the magnetoresistance effectelement 20 are different in shape, the laminate is processed in onedirection to obtain the wiring 30, and then the laminate is processed ina direction different from that direction. An ion milling method or areactive ion etching (RIE) method can be used for processing thelaminate.

Then, as illustrated in FIG. 8 (c), in order to protect a side surfaceof the magnetoresistance effect element 20, an outer circumference ofthe magnetoresistance effect element 20 is covered with an insulator 50.At this time, an exposed surface 50 a of the insulator 50 and an exposedsurface 27 a of the process protection layer 27 are not necessarilyformed at exactly the same position. Even if a film thickness iscontrolled when the insulator 50 is formed, a slight step may remainbetween respective surfaces. Further, the exposed surface 27 a of theprocess protection layer 27 is rough due to damage caused when thelaminate is processed.

Therefore, as illustrated in FIG. 8 (d), the exposed surface 50 a of theinsulator 50 and the exposed surface 27 a of the process protectionlayer 27 are polished. As the polishing method, chemical-mechanicalpolishing (CMP) is preferably used. The process protection layer 27 isremoved by polishing, and the cap layer 24 is exposed. The polishing isnot necessarily required to stop at an interface between the processprotection layer 27 and the cap layer 24, and may be stopped at a stagein which the cap layer 24 is polished to some extent.

By polishing, the exposed surface 50 a of the insulator 50 and anexposed surface 24 a of the cap layer 24 are on the same plane. Theexposed surface 24 a of the cap layer 24 is also flat, unlike theexposed surface 27 a of the process protection layer 27 before thepolishing.

Finally, the spin-orbit torque wiring 40 is laminated on the planarizedexposed surface. The spin-orbit torque wiring 40 is processed to extendin a direction intersecting the wiring 30. Thereafter, an exposedsurface of the spin-orbit torque wiring 40 is protected with theinsulator, and thereby a spin current magnetization rotationalmagnetoresistance effect element is manufactured.

It is important in this manufacturing method that the exposed surface 24a of the cap layer 24 on which the spin-orbit torque wiring 40 islaminated be planarized. An SOT induced by a pure spin current isgreatly affected by an interface effect of a lamination surface.Therefore, the SOT can be efficiently induced by planarizing the exposedsurface 24 a on which the spin-orbit torque wiring 40 is laminated.

A degree of orientation of magnetization of the second ferromagneticmetal layer 23 is also greatly affected by the lamination interface. Forexample, in the case of a perpendicular magnetization film,magnetization of the second ferromagnetic metal layer 23 is orientedperpendicular to the lamination interface. If the lamination interfaceis not flat, the magnetization is oriented to be slightly inclined withrespect to the lamination direction. When an orientation direction ofmagnetization varies, it causes a decrease in magnetoresistance (MR)ratio.

In this manufacturing method, it is also important that an object beingpolished not be the second ferromagnetic metal layer 23. For example,when only planarization of the lamination surface on which thespin-orbit torque wiring 40 is laminated is considered, it is alsoconceivable that the second ferromagnetic metal layer 23 is laminatedthick and an exposed surface of the second ferromagnetic metal layer 23is polished. However, when the second ferromagnetic metal layer 23 isformed thick, variations occur in characteristics thereof. In contrast,by providing the process protection layer 27 serving as a layer that isconfigured to be removed from the beginning, processing such aspolishing can be performed without imparting an influence on the secondferromagnetic metal layer 23.

As illustrated in FIGS. 3 to 6, when the spin-orbit torque wiring 40 isdivided into a spin current generation part 41 and low resistance parts42A and 42B, known processing means such as photolithography or the likecan be used.

In this case, it is preferable that the spin current generation part 41be formed before the low resistance parts 42A and 42B. This is so thatthe interface between the spin current generation part 41 and themagnetoresistance effect element 20 is not damaged in order to inhibitscattering of the pure spin current supplied from the spin currentgeneration part 41 to the magnetoresistance effect element 20.

(Operation of Spin Current Magnetization Rotational MagnetoresistanceEffect Element)

Next, an operation of the spin current magnetization rotationalmagnetoresistance effect element will be described. The spin currentmagnetization rotational magnetoresistance effect element outputsmagnetization rotation of the second ferromagnetic metal layer 23 as achange in resistance value. Hereinafter, as a method for performing themagnetization rotation of the second ferromagnetic metal layer 23, amethod using both of a spin transfer torque (STT) and the SOT, and amethod using only the SOT will both be described.

First, a method of performing the magnetization rotation of the secondferromagnetic metal layer 23 using both the STT and the SOT will bedescribed. FIG. 9 is a schematic cross-sectional view of the spincurrent magnetization rotational magnetoresistance effect elementaccording to the present embodiment taken along an xz plane. FIG. 9corresponds to a cross-sectional view in the xz plane. An insulator thatis unnecessary for understanding the operation of the element is omittedin the illustration.

As illustrated in FIG. 9, there are two kinds of currents in the spincurrent magnetization rotational magnetoresistance effect element 100.One is a current I₁ (STT inversion current) flowing through themagnetoresistance effect element 20 in a lamination direction andflowing through the spin-orbit torque wiring 40 and the wiring 30. InFIG. 9, the current I₁ flows in the spin-orbit torque wiring 40, themagnetoresistance effect element 20, and the wiring 30 in that order. Inthis case, electrons flow in the wiring 30, the magnetoresistance effectelement 20, and the spin-orbit torque wiring 40 in that order.

Another is a current I₂ (SOT inversion current) flowing in an extendingdirection of the spin-orbit torque wiring 40. The current I₁ and thecurrent I₂ intersect each other (at a right angle), and a currentflowing through the magnetoresistance effect element 20 and a currentflowing through the spin-orbit torque wiring 40 are joined ordistributed at a part in which the magnetoresistance effect element 20and the spin-orbit torque wiring 40 are joined (a reference sign 24′indicates a junction on the side of the magnetoresistance effect element20 (cap layer 24), and a reference sign 40′ indicates a junction on theside of the spin-orbit torque wiring 40).

When a current I₁ flows, electrons having a spin oriented in a samedirection as magnetization of the first ferromagnetic metal layer (fixedlayer) 21 pass through the nonmagnetic layer 22 and are supplied to thesecond ferromagnetic metal layer 23 while the spin direction ismaintained. These electrons impart a torque (STT) which causesmagnetization M₂₃ of the second ferromagnetic metal layer (free layer)23 to rotate.

On the other hand, the current I₂ corresponds to the current Iillustrated in FIG. 2. That is, when the current I₂ flows, a first spinSi and a second spin S2 are both bent toward an end part of thespin-orbit torque wiring 40 and produce a pure spin current J_(s). Thepure spin current J_(s) is induced in a direction perpendicular to adirection in which the current I₂ flows. That is, the pure spin currentJ_(s) is generated in a z-axis direction or an x-axis direction in thedrawing. In FIG. 9, only the pure spin current J_(s) in the z-axisdirection contributing to a direction of the magnetization of the secondferromagnetic metal layer 23 is illustrated.

The pure spin current J_(s) generated in the spin-orbit torque wiring 40by flowing the current I₂ on a front side in the drawing diffuses andflows into the second ferromagnetic metal layer 23 via the cap layer 24.The spin that has flowed in affects the magnetization M₂₃ of the secondferromagnetic metal layer 23. That is, in FIG. 9, when a spin orientedin a −x direction flows into the second ferromagnetic metal layer 23, atorque (SOT) for rotating the magnetization M₂₃ of the secondferromagnetic metal layer 23 oriented in a +x direction is applied.

As described above, an SOT effect due to the pure spin current J_(s)generated by the current flowing through a second current path (currentI₂) is added to an STT effect caused by the current flowing through afirst current path (current I₁), and thereby the magnetization M₂₃ ofthe second ferromagnetic metal layer 23 is rotated.

In order to rotate the magnetization of the second ferromagnetic metallayer 23 only by the STT effect (that is, a current of only the currentI₁ flows), it is necessary to apply a voltage equal to or higher than apredetermined voltage to the magnetoresistance effect element 20.Although a typical driving voltage of a tunnel magnetoresistance (TMR)element is relatively small at several volts or less, the nonmagneticlayer 22 is an extremely thin film of about several nanometers, andinsulation breakdown may occur. When a voltage is continued to beapplied to the nonmagnetic layer 22, stochastically, a weak part (atwhich film quality is poor, a film thickness is thin, or the like) ofthe nonmagnetic layer is destroyed.

In contrast, when the STT effect and the SOT effect are simultaneouslyused, the voltage applied to the magnetoresistance effect element 20 canbe reduced. In addition, current density of the current flowing throughthe spin-orbit torque wiring 40 can also be reduced. When the voltageapplied to the magnetoresistance effect element 20 is reduced, aprobability of the insulation breakdown of the nonmagnetic layer 22decreases. Further, by reducing the current density of the currentflowing through the spin-orbit torque wiring 40, energy efficiency canbe enhanced.

Next, a method of rotating the magnetization of the second ferromagneticmetal layer 23 using only the SOT will be described. FIG. 10 is aschematic cross-sectional view of the spin current magnetizationrotational magnetoresistance effect element according to the presentembodiment taken along an xz plane. An insulator that is unnecessary forunderstanding the operation of the element is removed in theillustration. When only the SOT is used, since the wiring 30 isunnecessary, the spin current magnetization rotational magnetoresistanceeffect element 102 illustrated in FIG. 10 does not have the wiring 30.

When only the SOT is used, only the above-described current I₂ is used.As described above, the current I₂ causes the pure spin current J_(s) tobe generated, and the generated pure spin current J_(s) diffuses andflows into the second ferromagnetic metal layer 23 via the cap layer 24.The spin that has flowed in affects the magnetization M₂₃ of the secondferromagnetic metal layer 23.

That is, in FIG. 10, when a spin oriented in the −x direction flows intothe second ferromagnetic metal layer 23, the torque (SOT) for rotatingthe magnetization M₂₃ of the second ferromagnetic metal layer 23oriented in the +x direction is applied to rotate the magnetization ofthe second ferromagnetic metal layer 23.

The current density of the current flowing through the spin-orbit torquewiring 40 is preferably less than 1×10⁷ A/cm². When the current densityof the current flowing through the spin-orbit torque wiring 40 isexcessively large, heat is generated due to the current flowing throughthe spin-orbit torque wiring 40. The heat reduces stability of themagnetization M₂₃ of the second ferromagnetic metal layer 23.

The deterioration in stability of the magnetization M₂₃ of the secondferromagnetic metal layer 23 increases the likelihood of magnetizationrotation due to an unexpected external force. Magnetization rotationleads to rewriting of recorded information. Therefore, from thisperspective, it is preferable to reduce the current flowing through thespin-orbit torque wiring 40, and it is preferable to use the methodusing both the STT and the SOT for magnetization rotation of the secondferromagnetic metal layer 23.

FIG. 11 is a schematic view illustrating the spin current magnetizationrotational magnetoresistance effect element according to the presentembodiment including a power supply. The spin current magnetizationrotational magnetoresistance effect element 100 illustrated in FIG. 11rotates the magnetization of the second ferromagnetic metal layer 23using both the STT and the SOT.

A first power supply 110 is connected to the wiring 30 and thespin-orbit torque wiring 40. The first power supply 110 controls acurrent flowing in the lamination direction of the spin currentmagnetization rotational magnetoresistance effect element 100. A knownpower supply can be used for the first power supply 110.

A second power supply 120 is connected to both ends of the spin-orbittorque wiring 40. The second power supply 120 controls a current flowingin a direction perpendicular to the lamination direction of themagnetoresistance effect element 20. That is, the second power supply120 controls the current flowing through the spin-orbit torque wiring40. A known power supply can be used for the second power supply 120.

As described above, the current flowing in the lamination direction ofthe magnetoresistance effect element 20 induces an STT. In contrast, thecurrent flowing through the spin-orbit torque wiring 40 induces an SOT.Both the STT and the SOT contribute to magnetization rotation of thesecond ferromagnetic metal layer 23.

In this manner, when an amount of the current flowing in the laminationdirection of the magnetoresistance effect element 20 and an amount ofthe current flowing in the direction perpendicular to the laminationdirection are controlled by the two power supplies, a contribution ratioof the SOT and the STT contributing to the magnetization rotation can befreely controlled.

For example, when a large current cannot flow through the device,control is performed such that the STT with high energy efficiency formagnetization rotation is mainly used. That is, the amount of currentflowing from the first power supply 110 is increased, and the amount ofcurrent flowing from the second power supply 120 is reduced.

Also, for example, when it is necessary to manufacture a thin device anda reduction in the thickness of the nonmagnetic layer 22 is inevitable,the current flowing through the nonmagnetic layer 22 is required to bereduced. In this case, the amount of current flowing from the firstpower supply 110 is reduced, the amount of current flowing from thesecond power supply 120 is increased, and then the contribution ratio ofSOT is increased.

When the magnetization of the second ferromagnetic metal layer 23 isrotated using only the SOT, the wiring 30 and the first power supply 110in FIG. 11 are unnecessary.

As described above, according to the spin current magnetizationrotational magnetoresistance effect element of the present embodiment,even in the magnetoresistance effect element using the SOT with a bottompin structure, scattering of the spin by the cap layer can be inhibited.Further, by using the process protection layer that is removed duringprocessing, the interface between the cap layer and the spin-orbittorque wiring can be planarized. That is, the pure spin currentgenerated in the spin-orbit torque wiring can be efficiently supplied tothe second ferromagnetic metal layer. Further, by providing thediffusion prevention layer, it is possible to prevent elements formingthe cap layer from diffusing into the second ferromagnetic metal layerand lowering the MR ratio.

REFERENCE SIGNS LIST

-   -   10 Substrate    -   20, 25 Magnetoresistance effect element    -   21 First ferromagnetic metal layer    -   22 Nonmagnetic layer    -   23 Second ferromagnetic metal layer    -   24 Cap layer    -   27 Process protection layer    -   30 Wiring    -   40 Spin-orbit torque wiring    -   41, 41A, 41B Spin current generation part    -   42A, 42B, 42C Low resistance part    -   50 Insulator    -   1 Current    -   S1 First spin S1    -   S2 Second spin    -   100, 101, 102 Spin current magnetization rotational        magnetoresistance effect element

1. A spin current magnetization rotational magnetoresistance effectelement comprising: a substrate; a magnetoresistance effect elementprovided on the substrate and including a first ferromagnetic metallayer in which a direction of magnetization is fixed, a nonmagneticlayer, a second ferromagnetic metal layer configured for a direction ofmagnetization to be changed, and a cap layer in an order from thesubstrate side; and a spin-orbit torque wiring extending in a directionintersecting a lamination direction of the magnetoresistance effectelement and joined to the cap layer, wherein the cap layer includes oneor more substances selected from the group consisting of Cu, Ag, Mg, Al,Si, Ge, and GaAs as a major component.
 2. The spin current magnetizationrotational magnetoresistance effect element according to claim 1,wherein a thickness of the cap layer is equal to or less than a spindiffusion length of a substance constituting the major component of thecap layer.
 3. A spin current magnetization rotational magnetoresistanceeffect element comprising: a magnetoresistance effect element includinga first ferromagnetic metal layer in which a direction of magnetizationis fixed, a nonmagnetic layer, a second ferromagnetic metal layerconfigured for a direction of magnetization to be changed, and a caplayer in an order; and a spin-orbit torque wiring extending in adirection intersecting a lamination direction of the magnetoresistanceeffect element and joined to the cap layer, wherein the cap layer hasspin conductivity, and the magnetoresistance effect element furtherincludes a diffusion prevention layer between the second ferromagneticmetal layer and the cap layer.
 4. The spin current magnetizationrotational magnetoresistance effect element according to claim 3,wherein the diffusion prevention layer has at least one selected from amagnetic element and an element having an atomic number equal to orhigher than that of yttrium.
 5. The spin current magnetizationrotational magnetoresistance effect element according to claim 3,wherein a thickness of the diffusion prevention layer is equal to orless than four times an atomic radius of an atom constituting thediffusion prevention layer.
 6. The spin current magnetization rotationalmagnetoresistance effect element according to claim 1, wherein thespin-orbit torque wiring includes a nonmagnetic metal having an atomicnumber of 39 or higher having a d electron or an f electron in anoutermost shell.
 7. The spin current magnetization rotationalmagnetoresistance effect element according to claim 1, wherein thespin-orbit torque wiring is made of: a pure spin current generation partmade of a material that generates a pure spin current; and a lowresistance part made of a material having electric resistance lower thanelectrical resistance of the pure spin current generation part, and atleast a part of the pure spin current generation part is in contact withthe cap layer.
 8. A magnetic memory comprising a plurality of spincurrent magnetization rotational magnetoresistance effect elementsaccording to claim
 1. 9. A method of manufacturing a spin currentmagnetization rotational magnetoresistance effect element comprising thesteps of: forming a laminate in which a first ferromagnetic metal layerin which a direction of magnetization is fixed, a nonmagnetic layer, asecond ferromagnetic metal layer configured for a direction ofmagnetization to be changed, a cap layer, and a process protection layerare laminated in an order on a substrate; processing the laminate into apredetermined shape to form a magnetoresistance effect element; andremoving the process protection layer and forming a spin-orbit torquewiring on an exposed surface exposed after the removal.
 10. The spincurrent magnetization rotational magnetoresistance effect elementaccording to claim 4, wherein a thickness of the diffusion preventionlayer is equal to or less than four times an atomic radius of an atomconstituting the diffusion prevention layer.
 11. The spin currentmagnetization rotational magnetoresistance effect element according toclaim 2, wherein the spin-orbit torque wiring includes a nonmagneticmetal having an atomic number of 39 or higher having a d electron or anf electron in an outermost shell.
 12. The spin current magnetizationrotational magnetoresistance effect element according to claim 3,wherein the spin-orbit torque wiring includes a nonmagnetic metal havingan atomic number of 39 or higher having a d electron or an f electron inan outermost shell.
 13. The spin current magnetization rotationalmagnetoresistance effect element according to claim 4, wherein thespin-orbit torque wiring includes a nonmagnetic metal having an atomicnumber of 39 or higher having a d electron or an f electron in anoutermost shell.
 14. The spin current magnetization rotationalmagnetoresistance effect element according to claim 5, wherein thespin-orbit torque wiring includes a nonmagnetic metal having an atomicnumber of 39 or higher having a d electron or an f electron in anoutermost shell.
 15. The spin current magnetization rotationalmagnetoresistance effect element according to claim 10, wherein thespin-orbit torque wiring includes a nonmagnetic metal having an atomicnumber of 39 or higher having a d electron or an f electron in anoutermost shell.
 16. The spin current magnetization rotationalmagnetoresistance effect element according to claim 2, wherein thespin-orbit torque wiring is made of: a pure spin current generation partmade of a material that generates a pure spin current; and a lowresistance part made of a material having electric resistance lower thanelectrical resistance of the pure spin current generation part, and atleast a part of the pure spin current generation part is in contact withthe cap layer.
 17. The spin current magnetization rotationalmagnetoresistance effect element according to claim 3, wherein thespin-orbit torque wiring is made of: a pure spin current generation partmade of a material that generates a pure spin current; and a lowresistance part made of a material having electric resistance lower thanelectrical resistance of the pure spin current generation part, and atleast a part of the pure spin current generation part is in contact withthe cap layer.
 18. The spin current magnetization rotationalmagnetoresistance effect element according to claim 4, wherein thespin-orbit torque wiring is made of: a pure spin current generation partmade of a material that generates a pure spin current; and a lowresistance part made of a material having electric resistance lower thanelectrical resistance of the pure spin current generation part, and atleast a part of the pure spin current generation part is in contact withthe cap layer.
 19. The spin current magnetization rotationalmagnetoresistance effect element according to claim 5, wherein thespin-orbit torque wiring is made of: a pure spin current generation partmade of a material that generates a pure spin current; and a lowresistance part made of a material having electric resistance lower thanelectrical resistance of the pure spin current generation part, and atleast a part of the pure spin current generation part is in contact withthe cap layer.
 20. The spin current magnetization rotationalmagnetoresistance effect element according to claim 6, wherein thespin-orbit torque wiring is made of: a pure spin current generation partmade of a material that generates a pure spin current; and a lowresistance part made of a material having electric resistance lower thanelectrical resistance of the pure spin current generation part, and atleast a part of the pure spin current generation part is in contact withthe cap layer.